Electronic circuit systems are typically made by defining complex integrated circuit structures in semiconductor chips, bonding the chips to circuit package subsrtates, and in turn bonding the packages to printed circuit boards. For interconnection and structural bonding, increased use is being made of "flip chip" technology, in which an integrated circuit chip is soldered directly to the surface of a substrate with the conductor pattern of the chip facing the substrate. In accordance with known "surface mounting" techniques, a plurality of solder "bumps" are formed on either or both the chip and the substrate, and the bonding is made by heating the structure to melt (or reflow) the solder so that, when the solder hardens, the chip is bonded to the substrate. The bonded portions electrically interconnect circuits on the chip and the substrate as well as structurally bonding them.
When the device package comprises a ceramic substrate upon which a circuit has been defined that makes connection with several chips mounted on it, the result is usually referred to as a hydrid integrated circuit (HIC). To accommodate the higher circuit density of modern chips, there has arisen a demand for more complex circuitry on the substrate that can conveniently be made on a ceramic substrate. To meet these demands, workers have developed silicon substrates upon which denser circuit patterns of two or more levels can be formed: such packages are still generally in the developmental stage and are sometimes known as advanced VLSI packaging (AVP).
An AVP package may typically comprise many chips each connected by a multiplicity of solder bonds to a substrate to form with the substrate a complex system or subsystem. Because of the complexity of the chips and of the circuit as a whole, after the circuit package has been assembled, it is frequently found that one of the chips must be removed for repair or replacement. This can be done by either shearing or melting the solder bonds, removing the chip, and then rebonding a replacement or repaired chip using the surface mount techniques described previously. It is obvious that shearing the solder bonds would be a difficult and tedious task which would be likely to damage the substrate. Melting all of the solder bonds on the substrate might be harmful to interconnections to chips that are not to be removed. It has therefore been clear for some time that there is a need for apparatus and methods for expediting the selective removal of integrated circuit devices which are solder bonded at a multiplicity of points to a substrate. It is important that such removal be made in such a manner that one does not cause spurious short circuits betwen adjacent bonding pads of the substrate and such that remnant solder can be expediently removed after chip removal.